1. Field of the Invention
This invention relates to a process for the manufacture of stable polymer polyol dispersions with a narrow distribution of particle sizes prepared by the precipitation polymerization of polyepoxides with epoxide resin hardeners in the presence of polyols.
2. Description of the Prior Art
The use of polyamines, particularly diamines, for cross-linking polyepoxides, for example, epoxy adhesives or lacquers, paints, and varnishes is part of the current state of the art. The hardening process is advantageously carried out in the absence of solvents. If required, volatile solvents, which are inert under the reaction conditions, are used.
The production of polyaddition products from diisocyanates and bifunctional amines, hydrazines and hydrazides, in high molecular weight polypropylene glycol ethers containing at least two hydroxyl groups has also been taught. Such dispersions are suitable as thickening pastes in textile or dying auxiliaries. For other areas of application, the high viscosity and the limited stability are drawbacks, particularly for ease of processability. In order to reduce these difficulties, it has been recommended that the polyaddition reaction be conducted in continuous flow-through mixers with high mixing output.
While the primary reaction occurs between the NCO and NH.sub.2 groups, the secondary reaction between the hydroxyl-group containing polyols and the polyisocyanate cannot be totally eliminated. This reaction results in polymer polyol dispersions of various compositions which either can not be reproduced or are very difficult to reproduce. Another drawback is the irregular form of the polymer and the wide particle size distribution of the polymer as well as the relatively high viscosity of the dispersion which is usually greater than 2,500 centipoises in a 10 percent dispersion at 25.degree. C.
The purpose of this invention was to produce stable polymer polyol dispersions with low viscosities in which the dispersed polymer particles are chemically and morphologically uniform, in which the average polymer particle diameters are small, and in which the polymer particle size distribution is narrow.
This task is met by a process for the manufacture of stable polymer polyol dispersions with narrow particle size distribution by means of precipitation polymerization wherein the polyepoxides are reacted with epoxide resin hardeners in the presence of polyols which are liquid at reaction temperatures.